The present invention pertains to the field of art involving enhancement of the analog signal information received from a sensor prior to converting the analog signal to digital form.
A typical application of this invention is in an endoscope/borescope that is equipped with a video readout for providing television pictures of a remote target. As explained in greater detail in U.S. Pat. Nos. Reissue 31289 and Reissue 31290 to Moore et al., it is now possible with solid state image sensors sometimes referred to as charge coupled devices (CCD) to provide the insertion head of an endoscope/borescope with an extremely small video camera permitting access to extremely confined regions that have heretofore been inaccessible. Full color video pictures of the target can be created using a single imager by illuminating the targets sequentially with light of primary colors to produce color separated images. After each color separated image is recorded, image data is clocked out in the form of video signals and delivered to a video processor where the combined data is placed in a form that is suitable for display on a television screen.
As is well known in the art, the viewing head of an endoscope/borescope is mounted at the distal end of the insertion tube and is generally required to operate within a very confined area with little if any ambient light. Light is generally brought into the image region by means of a fiber optic bundle. As the head moves towards or away from a given target situated in this confined region the amount of light reflected from the target to the image sensor will vary substantially. Although automatic light control and automatic gain control circuits have been included in the video section of these instruments, this in itself may not be sufficient to allow retrieval of all the information contained in the image signal i.e. the sensor may become saturated with light (blooming) or remain dark or otherwise provide an image that is difficult to read in complete detail. A further problem is sometimes encountered with weak video signals whereby background noise becomes visible and obscures the desired image.